number.round

gistfile1.txt

String.prototype.lpad = function (padding, length) {
    var string = this;
    while (string.length < length) {
        string = padding + string;
    }
    return string;
}

Number.prototype.round = function(base) {
    if (base == null || base < 0) {
        return this;
    }
    
    var string = this.toString();
    var point_index = string.indexOf(".");
    if (point_index == -1) {
        return this;
    }
    var symbol_index = point_index + 1 + base;
    if (symbol_index >= string.length) {
        return this;
    }
    
    var integer        = parseInt(string.substring(0, point_index), 10);
    var fractional     = parseInt(string.substring(point_index + 1, point_index + 1 + base), 10) || 0;
    var max_fractional = Math.pow(10, base);
    var symbol         = parseInt(string.charAt(symbol_index), 10);
    if (symbol >= 5) {
        if (base == 0) {
            integer ++;
        } else {
            if (fractional + 1 == max_fractional) {
                integer ++;
                fractional = 0;
            } else {
                fractional ++;
            }
        }
    }
    
    return new Number(parseFloat(integer + "." + (fractional.toString().lpad("0", base))));
}